Lecture 4 - Introduction to Protozoology

• Protozoans are an extremely diverse assortment of unicellular eukaryotes.
• Protozoa

  • Lack a cell wall
  • Have at least one motile stage in life cycle
  • Most ingest their food
• Autotrophs - contain chloroplasts.
• Heterotrophs - absorb organic molecules or

  ingest larger food particles.

  • Phagocytosis
• Mixotrophs - combine photosynthesis and heterotrophic nutrition.
• Free-living and symbiotic species.

  • Mutualistic – benefits both.
  • Commensalistic – one benefits, the other is neutral.
  • Parasitic – one benefits at a cost to the other.
• Others use ameboid movement to get around.

  • A pseudopod is extended forward, followed by the rest of the organism.
• Pseudopodia are extensions of the cell cytoplasm used for locomotion.
• • Nucleus – contains DNA.
  • Mitochondria – organelle used in energy production.
  • Golgi – part of the secretory system of the ER.
• • Plastids – organelles containing photosynthetic pigments.
  • Extrusomes – organelles that extrude something from the cell.
• Holozoic feeders, or phagotrophs, ingest particles of food.

  • Food vacuole – the membrane-bound vesicle containing the food.
• Contractile vacuoles fill with fluid and then

  expel the fluid outside the cell.

  • Function in osmoregulation.
• Fission is the cell multiplication process in protozoa.

  • Binary fission – one individual splits into two equal sized individuals.
  • Budding – progeny cell much smaller than parent.
  • Multiple fission – multiple nuclear divisions followed by multiple cytoplasmic divisions producing several offspring.
• Many protists are able to survive harsh

  conditions through the formation of cysts, dormant forms with resistant outer coverings and a shutdown of metabolism.
• Opisthokonta is a very large clade characterized by a combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells.
• The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae.
• The clade Viridiplantae contains unicellular

  and multicellular green algae, bryophytes and vascular plants.
• Phylum Chlorophyta – single celled algae colonial forms.
• Phylum Euglenozoa is a diverse clade that includes

  predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. Kinetoplastids & Euglenids.
• Euglenids have one or two flagella that emerge from a pocket at one end of the cell.
• Kinetoplastids have a single, large mitochondrion that contains an organized mass of DNA called a

  kinetoplast.
• Phylum Retortamonada includes commensal and parasitic unicells.

  • Lack mitochondria & Golgi
• Diplomonads have two nuclei and multiple flagella.

  • Giardia
  • Are adapted to anaerobic environments.
  • Lack plastids.
  • Lack mitochondria but may have mitochondrial genes in the nucleus.
• Members of the clade Alveolata have membrane-

  bounded sacs (alveoli) just under the plasma

  membrane.
• Members of the phylum Ciliophora use cilia to move and feed.
• Ciliates are a large, varied group of protists.
• All ciliates have a kinety system made up of the cilia, kinetosomes and other fibrils.
• Alveolata - Ciliates

  Many have structures that can be expelled such as trichocysts and toxicysts.
• Suctorians – ciliates that lose cilia as adults, grow a stalk and become sessile.

  • Use tubelike tentacles for feeding.
• Symbiotic ciliates – some commensal, others parasitic.
• Free-living ciliates – may be swimmers, or sessile.

  • Stentor, Vorticella, Paramecium
• Paramecium, as well as many other protists, reproduce asexually by binary fission.
• Conjugation is a sexual process that produces genetic variation.
• Conjugation is separate from reproduction

  which generally occurs by binary fission.
• Phylum Dinoflagellata is a diverse group of aquatic photoautotrophs and heterotrophs.

  • Abundant in both marine and freshwater phytoplankton.
• Apicomplexans are parasites of animals and some cause serious human diseases.
• Have a non-photosynthetic plastid, the apicoplast.
• Parabasalids move by means of flagella and an undulating part of the plasma membrane.

  • This clade may have diverged from the main eukaryotic clade very early.
  • Trichomonas
• Amebas are found in fresh and salt water as well as moist soil.

  • feeds by wrapping a pseudopod around its food – phagocytosis.
• Nonactinopod amebas include amebas that form lobopodia, filipodia or rhizopodia.

  • Mostly heterotrophic and actively seek and consume bacteria and other protists.